The invention provides cross-linked polymeric films, laminates, membranes or other polymeric articles, which show rubber like heat resistance (hot set) and dimensional stability above the polymer melting point, while maintaining heat sealing properties.
Thermoplastic films or articles are limited in their use at elevated temperatures, due to the respective melting behavior of their polymeric components. Thermoplastics are typically cross-linked to improve their thermal resistance, making them usable above their melting temperature. However, heat sealing properties and welding properties are lost when the polymer is cross-linked.
U.S. Pat. No. 4,851,290 discloses an irradiated three layer thermoplastic film comprising a nylon 6.12 or nylon 6.66 core layer, and outer layers comprising a blend of 50-75 percent polyethylene or EVA, and 25-50 percent of a polyethylene-modified adhesive or EVA-modified adhesive.
U.S. Pat. No. 5,055,328 discloses a tubular article formed of multilayer, differentially cross-linked heat sealable film. The multilayer film contains at least two layers, an inner layer and an outer layer. The inner layer is a heat sealable layer containing an antioxidant cross-linking inhibitor, in an amount sufficient to inhibit the cross-linking of that layer by irradiation. Upon exposure of the multilayer film to radiation, the outer layer is cross-linked to a greater extent than the first heat sealable layer.
European Patent Application EP0597502A2 discloses a heat-shrinkable, thermoplastic film or bag, which contains at least one homogeneous ethylene alpha-olefin copolymer having a density of at least 0.90 g/cc. Oriented films are disclosed as having improved optics and improved impact resistance. A homogeneous ethylene alpha-olefin copolymer may be present in a monolayer film, either alone, or in a blend, or may be included in one or more layers of a multilayer film.
United Kingdom Patent Application GB 1480204 discloses a laminated polymeric film comprising the following: (a) a film of nylon, (b) a film of a mono-alpha olefin polymer which is cross-linkable by radiation, and (c) an adhesive layer, comprising an organic polymer, disposed between these films, the polymer having cross-linkable olefin-derived units as the major component thereof. The laminated assembly is cross-linked to an extent equivalent to a radiation dosage absorbed by at least 6 Megarads for each of the specified films (a) and (b) and layer (c). The nylon may be polycaproamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polycaprylamide, polyundecanoamide or polydodecanamide. The mono-alpha olefin polymer may be polyethylene, polypropylene, polybutene-1, or an ethylene/vinylacetate copolymer. The polymeric adhesive may be a homopolymer, a copolymer, a terpolymer, a block copolymer, a graft copolymer, or an ionomeric copolymer.
International Publication No. WO 2006/031172 discloses a strip tape having the following layers: a first layer with an outwardly facing surface of polypropylene (PP); a first adhesive layer, a core layer of an oxygen barrier polymer, a second adhesive layer, a second layer with an outwardly facing surface of polypropylene (PP).
Additional films, articles, and/or rheology modified compositions are disclosed in the following references: EP 0577432A1, U.S. Pat. No. 4,283,630, GB 2233934A, U.S. Pat. No. 4,064,296, GB 2099755A, U.S. Pat. No. 4,240,993, GB 1383556, U.S. Pat. No. 4,246,709, GB 2083403A, WO 96/33923, WO 97/22536, US 2006/0003123, US 2006/0000545, US 2006/0032120, US 2006/0003122, EP 1216146B1, WO 96/38288, WO 98/18841, WO 95/32095, WO 98/32795, WO 02/24803, WO 05/056670, and WO 06/124396.
None of the conventional art provides for polymeric films and articles that have characteristics of a thermoset/crosslinked article, while maintaining weldability and sealability. Thus, there is a need for polymeric films and articles, which are dimensionally stable above the polymer melting point, and which maintain heat sealing and/or welding properties. In particular, there is a need for crosslinked films with thermoset heat resistance (no melting), improved mechanical properties, and improved puncture resistance. There is a further need for such crosslinked films that maintain heat sealing properties and heat welding properties, while maintaining dimensional stability during the sealing or welding step. There is an additional need for crosslinked films with a broad and reliable heat sealing window, and which can be used in high temperature filling and processing applications, in heat or radiation sterilization, and in stretch film and shrink film applications. Some of these needs and others have been met by the following invention.